Conventionally, as an illuminating means for a liquid crystal display monitor used in a personal computer, a television and the like, a surface light source apparatus using a plurality of light emitting diodes (LEDs) as spot light sources is known.
With a surface light source apparatus, a plurality of LEDs are arranged in a matrix pattern in the back surface of a flat diffusing member having virtually the same shape as a liquid crystal display panel of a liquid crystal display monitor. The surface light source apparatus allows lights emitted from the LEDs to be incident inside the diffusing member from the back surface of the diffusing member, and emits the lights incident inside the diffusing member, from the emission surface facing the back surface of the diffusing member. The surface light source apparatus can perform planar illumination of the liquid crystal display panel by these emission lights.
Further, a light emitting apparatus that combines LEDs with lens bodies and that controls traveling directions of lights emitted from the LEDs, by the lens bodies is known. This light emitting apparatus requires a configuration for adjusting the positions of the lens bodies with respect to the LEDs.
Patent Literature 1 discloses a lens body formed with a lens part and a position adjusting part that is made of an elastic material and that adjusts the position of the lens part with respect to the LED. A fitting part that fits with the LED substrate is formed in this position adjusting part. Compared to the case where a lens part and a position adjusting part are integrally made of, for example, a PMMA (poly(metylo methacrylate)) material, the invention of Patent Literature 1 solves the problem that the lens body is broken by the stress concentrated on the fitting part, and makes it easy to manufacture lens bodies and adjust the positions of the lens bodies.
Further, Patent Literature 2 discloses a light emitting apparatus that controls traveling directions of lights emitted from light emitting elements (i.e. LEDs) by light flux controlling members. This Patent Literature 2 does not mention to a method of fixing the light flux controlling members to LED substrates.
FIG. 1 is a plan view of a surface light source apparatus forming a conventional display apparatus disclosed in Patent Literature 2, where an object-to-be-illuminated of, for example, a liquid crystal display panel is removed. FIG. 2 is a cross-sectional view of a display apparatus cut along X1-X1 line of FIG. 1.
As shown in FIG. 1, surface light source apparatus 1 has: flat light diffusing member 2 that is arranged in the back surface of an object-to-be-illuminated such as a liquid crystal display panel and that has virtually the same shape as the object-to-be-illuminated; a plurality of light emitting elements 3 of spot light sources that are arranged at pitches P of virtually equal intervals on the back surface of light diffusing member 2; and light flux controlling members 4 that control the traveling directions of lights emitted from light emitting elements 3.
Above light emitting element 3 and light flux controlling member 4 form light emitting apparatus 5.
As shown in FIG. 2, display apparatus 6 is formed with surface light source apparatus 1; and object-to-be-illuminated 7 arranged on the emission surface 8 (the surface opposite to back surface 9) side of light diffusing member 2.
Light diffusing member 2 is formed in a sheet shape or a planar flat shape using a resin material such as PMMA (poly(metylo methacrylate)) or PC (Polycarbonate) having superior optical transparency. Light diffusing member 2 is formed in virtually the same size as a planar shape of the object-to-be-illuminated such as a liquid crystal display panel, an advertisement display panel and a signpost display panel.
In light diffusing member 2, fine concavities and convexities (prism projections, or concavities and convexities formed by diffusing processing such embossing treatment or beads coating) are formed on its surface, or, inside light diffusing member 2, a diffusing member is mixed.
Light diffusing member 2 allows transmission of lights emitted from light controlling emission surfaces 11 of light flux controlling members 4 and diffuses the lights, and makes the lights radiated on the object-to-be-illuminated uniform.
Light emitting elements 3 are, for example, LEDs. Light emitting elements 3 are arranged in a matrix pattern in the back surface of light diffusing member 2.
Light flux controlling member 4 is an expanding lens that controls the traveling direction of a light emitted from light emitting element 3, and is, for example, an aspheric lens. Light flux controlling member 4 is made of, for example, a transparent resin material such as PMMA (poly(metylo methacrylate)), PC (polycarbonate), and EP (epoxy resin), or a transparent glass.
Light flux controlling member 4 has: light controlling emission surface 11 that has a virtually circular planar shape and that controls the traveling direction of a light emitted from light emitting element 3; concavity 13 that allows incidence of a main beam including lights emitted in the direction of the reference optical axis among lights emitted from light emitting element 3; and back surface 12 that radially extends from the opening rim part of this concavity 13 and that allows incidence of a subbeam emitted from light emitting element 3 at a large angle with respect to the reference optical axis. Further, light flux controlling member 4 has flange upper surface 14a of a virtually annular shape that projects outward of the radial direction of light controlling emission surface 11; flange lateral surface 14b that connects the outer rim part of flange upper surface 14a and the outer rim part of back surface 12; and leg parts 15 of a round stick shape that attach light flux controlling member 4 in a state where the position of light flux controlling member 4 is determined with respect to base plate 17. The portion surrounded by back surface 12, flange upper surface 14a, flange lateral surface 14b and a virtual surface (i.e. the inner peripheral surface of flange 14) that passes the inner rim part of flange upper surface 14a and that is orthogonal to back surface 12, is flange 14, and the area of flange 14 of back surface 12 is lower flange surface 14c. 
Light controlling emission surface 11 is projected higher (toward light diffusing member 2) than flange upper surface 14a. 
Leg parts 15 fix light flux controlling member 4 to surface 17a of substrate 17 in a predetermined position and at a height, and three leg parts 15 are formed at equal intervals in lower flange surface 14c. Leg parts 15 are glued by adhesive 16 (see FIG. 3(b) described later) in a state where the position of light flux controlling member 4 is determined with respect to surface 17a of substrate 17.
Legs 15 are made of the same material and formed integrally with light flux controlling member 4.
When light flux controlling member 4 is attached to substrate 17, gap ε is formed between the light emission surface of light emitting element 3 and back surface 12 of light flux controlling member 4. Gap ε is formed to, for example, discharge heat discharged from light emitting element 3, from gap ε in a state where light flux controlling member 4 is placed on substrate 17 such that light emitting element 3 is accommodated in concavity 13.
FIG. 3 explains the influence when leg parts 15 of light flux controlling member 4 are glued to surface 17a of substrate 17, and FIG. 3(a) is a plan view of light flux controlling member 4 seen from above and FIG. 3(b) is a magnified view of leg part 15 of FIG. 3(a).
As shown in FIG. 3(a), three leg parts 15 are formed at equal intervals in lower flange surface 14c (see FIG. 2), and are glued to surface 17a of substrate 17 by adhesive 16 (see FIG. 3(b)).
Adhesive 16 is made from a thermoset resin, and fixes leg parts 15 on substrate 17 by hardening the resin by heat. For this use, a black thermoset adhesive that hardens at a predetermined temperature and that provides a sufficient adhesive strength is known.